Anyone tried to make BIG dish at home?

[BombedOne]

Hello. I want to get big, and have large dish for satellite. The problem is - THE PRICE & availability. Each cm size increase, almost doubles price. Just check local ones:

120cm - $25
150cm - $45
180cm - $85
200cm - $200
240cm - $570

All these are solid dishes for Ku, no mesh or segment ones for C.

I've researched various books and internet sites, and found some interesting results:

1. small sized (40-60cm) dishes can be made at home in 1-2 hour, with minimum materials required.

2. Some russian websites show selfmade offset panels, but they are aimed for multi-satellite reception, not for fringe zones, and also, involve huge amount of machinery.

3. In one book, I found most reasonable (in pricing and difficulty) method of making prime focus dish out of epoxy and fiber glass. But unfortunatelly, it only quotes dimensions of preform needed for 2m dish manufacture, saying that calculations are too complex (it lists all formulas, but I got lost in them), so better use predefined values and made 2m one.

So here's questions:

1. Does anyone ever made dish by himself,
2. and, was it bigger than 2m ?
3. If done it, how, which method was used?

Thanks in advance.

 

[Robbo]

Don't you just need the formula for a parabola?

_http://www.intmath.com/Plane-analytic-geometry/4_Parabola.php

 

[trigger]

Have you seen the German guy that made an 8Mdish in south America. Look on this forum and then I think he has a website too

 

[Robbo]

That'll be Klaus Schumacher in Brazil picking up 19E.

 

[T_G]

Hi
Some points to think about:

I had a look at this matter in the past, the problem when making a big dish is that you would need to first decide which material to use. If you were to use a ish made of a composite material you would need to make a mould first, and then make the dish from it. The problem is how do you do such a big mould, while keeping to the exact shape?? If you have access to CNC that machines Oreol ?? (forgot the name, some sort of wood-like plastic) and someone who knows how to program using 3D software you could theoretically machine all the parts in smaller pieces, and then assemble them to create the mould. SUch a large shape would be vey expensive in material of machining time.
Then the mould would need to be treated so the surface would not disintegrate (unless it is a one-off, but even then you would need to do some work on it).
The next problem would be to do the glass fibre work. It is not as easy as it looks, I was involved in designing and producing fairings for motorcycles (which are not as large) and there are several problems with such large surfaces. I believe that without using a vacuum bag to press the fibre against the mould you would get distortion when it cures. the best solution would be to cure it in an autoclave heated vaccum chamber. Also, such a large shape without the proper support would be very wobbly - you would either need to make it very thick, which creates other problems, or you would need to add strengthening pieces to the outside during the process all possible but you would need to have lots of experience with composite materials to know where to place what.
It is possible, for sure, but very difficult for a beginner. One possibility is to try to borrow an existing dish and use that as the template for a mould. But again, you would need to be quite good at this technique - not a beginners job.

Finally - you would need to build the support and the LNB brackets etc so that they are exactly where they need to be. The larger the dish and the heavier it is the more difficult it becomes to make sure the dish stays in the correct shape.

I am not sure how the signal quality would be affected by using glass fibre, but I suppose there are paints you could use, also there are glass fibre mats available which have metal fibres in them - that could work - I would do a test on a smaller dish first and compare the signal strength before deciding.

When making such a large dish you would use up quite a large amount of glass fibre matting, you would need probably 3 layers of matting, and a large quantity of resin and hardner - dont know the prices but not very cheap either.

At the end of the day you would have to do a lot of research, find someone who has done work with glass fibre before, who might be interested to do one for himself as well. Just imagine of you get it wong - you would ruin a lot of work just by getting the resin - hardner ratio wrong.

Might be cheaper to buy a second hand one...

TG

 

[divibi]

I am not sure how the signal quality would be affected by using glass fibre, but I suppose there are paints you could use, also there are glass fibre mats available which have metal fibres in them - that could work - I would do a test on a smaller dish first and compare the signal strength before deciding.

Hi,

Once you've got a mould, why not spread fine mesh on it and pour liquid plastic over it to encapsulate the shape of the mesh? Is it how Andrew offset dishes are made? What kind of plastic is it? I think it lets the microwaves through with no or minimal loss. What do you think?

 

[BombedOne]

Thanks everyone for reply.

Regarding method I've read in book. It has drawing for making specially cutted out metal plate, which you install on tube, to allow 360 degree rotation over center axis, and you use it to create preform from concrete and (or) clay. Below I tried to reproduce drawing from it:

_http://img329.imageshack.us/my.php?image=dishov4.jpg

First you make metal plate (The formula I mentioned defines it's shape calculation, and book already contains design for 2m dish plate), then mount it on stable pole. Then build pyramid like construction around of it made from bricks or stones. After that - roughly apply concrete, and start using metal plate to achieve exact form. For finishing touches, modelling clay is recomended. Regarding reflecting layer, it should be made from aluminum foil.

The real problem is, book doesn't mentions quantity of fiberglass and epoxy needed even for 2 meter model (trough it says - 5 or 6 layers will be needed). So if it really needs large amount, maybe manufacturing will be expensive, than buying ready one. For test purposes, I bought 0.5kg of epoxy and 1x1m sheet of fiberglass fabric. This weekend I'll try to reproduce small scale (20-30cm) model, just to check manufacturing problem/expenses, I will not target parabolic shape, just will use beach ball as preform.

Balancing LNB position won't be a hard task I think. Is it possible to adjust length of each support leg, so I can lock to some powerfull satellite, adjust legs to reach maximum signal, and then turn dish to weaker one.

 

[divibi]

Hi all,

BombedOne, thank you for starting this thread. My short term goal is to build a 50 - 80 cm parabolic dish out of cardboard and foil to experiment with the strongest signals, here on 5w, 28e and 39e. I have 3 questions;
1. those 40-60cm dishes you can build in 1 hour; are they cardboard and foil?
2. What is the title of the book you took the example from? Is that about microwave dx-ing?
3. VERY IMPORTANT to me; does fibreglass let microwaves through? Could you build, let's say a 50cm cardboard and foil dish and to freeze the shape apply epoxy resin (or something or plastic?) all around the dish to STIFFEN IT FOREVER IN A DESIRED SHAPE???
4. Maybe you know how much in $$$ is a SUPRAL offset dish 3700x4005 that has a funny shape? Is it one piece?
Thank you in advance.

 

[T_G]

Hi,

Once you've got a mould, why not spread fine mesh on it and pour liquid plastic over it to encapsulate the shape of the mesh? Is it how Andrew offset dishes are made? What kind of plastic is it? I think it lets the microwaves through with no or minimal loss. What do you think?

It sounds easier than it is - in my opinion. The big problem is getting a good mould, and preferably use it for several attempts as most likely the first one will be the one where you find out all the mistakes.
Then, you would need to get the mesh onto the mould in such a way so that there are no creases or folds etc. (and that it does not destroy the mould when removing the dish.) If you managed to do that, and also found a way making sure the mesh does not move during the process (remember that many resins or plastic liquid components generate heat when they cure, and also they do sometimes start to warp. Also, you can calculate the weight of the resin over the surface of the dish, even a few mm thickness of the resin + the mesh will be quite heavy) you got another problem - you can't just simply pour resin or plastic over it - gravity will make the resing run down the sides. Even if in the end there is enopugh resin there to keep the shape, you wold end up with vastly variying thicknesses, I don't know how this will effect the signal.

With normal glass fibre the problem of the resin running down is also present, but not as much.

Regarding method I've read in book. It has drawing for making specially cutted out metal plate, which you install on tube, to allow 360 degree rotation over center axis, and you use it to create preform from concrete and (or) clay. Below I tried to reproduce drawing from it:

_http://img329.imageshack.us/my.php?image=dishov4.jpg

First you make metal plate (The formula I mentioned defines it's shape calculation, and book already contains design for 2m dish plate), then mount it on stable pole. Then build pyramid like construction around of it made from bricks or stones. After that - roughly apply concrete, and start using metal plate to achieve exact form. For finishing touches, modelling clay is recomended. Regarding reflecting layer, it should be made from aluminum foil.

The real problem is, book doesn't mentions quantity of fiberglass and epoxy needed even for 2 meter model (trough it says - 5 or 6 layers will be needed). So if it really needs large amount, maybe manufacturing will be expensive, than buying ready one. For test purposes, I bought 0.5kg of epoxy and 1x1m sheet of fiberglass fabric. This weekend I'll try to reproduce small scale (20-30cm) model, just to check manufacturing problem/expenses, I will not target parabolic shape, just will use beach ball as preform.

I did not see your pictures as I can't be arsed to download them from file sites. Why don't you simply attach them here???

Making a mould using a rotating piece of metal and a pole is definetly possible. If you get the pole to be DEAD straight and the shape plate cut to the correct shape you could get a good shape. I would investigate the possibility of mounting the pole on a thick heavy surface plate and mount the pole on a bearing so that it is easy to rotate.

Using concrete: damn I hate concrete, heavy and dirty. I am trying to think of a better material. But very hard to get the very smooth surface, if you use modelling clay, you would need quite a lot and that is not cheap either. I suppose if you know someone who knows how to finish walls in your house, he could probably do a reasonably good job on this.

Very interesting, let's kep working on this 2

 

[BombedOne]

1. Those simple dishes are made really simple - just take beach ball, inflate it as hard as possible, to maintain shape (big transparent ones), self adhesive aluminum foil. cut foil in stripes, and attach them to ball to cover approx 30% of surface, in dish shape. Attach LNB to opposite end of ball - you're done.

2. The book is about Microwaves in general, this is old soviet book (issued around 1987), it's dedicated for students, studying microwave transmission, and that dish project is given as training project for students. I think this book will be floating over internet - I'll try to find it.

3. No it doesn't. So you need to apply epoxy to back side of dish.

4. Regarding "SUPRAL offset dish 3700x4005". This seems to be too big and too weird. Are you sure about dimensions? Also, Russian dishes are very expensive. If you willing to buy from outside, take look at china. For example, 6 panel 240cm dishes start from $35 (0.5mm steel) to $120 (0.9mm steel).

Regarding posting pictures and so on in this forum, it's quite hard, because this site works very strangely here. For example, I can't see my post for couple of hours, nor I can find "attach the file" link.

 

[BombedOne]

Selfmade 60cm offset dish, made from epoxy, old curtain and aluminum foil.

samodelki.ucoz.ru/news/2008-04-25-179

 

[divibi]

Does anybody know exactly how mr Klaus Schumacher built his 8 metre dish? I only know he had a negative concrete mould, that serves as a swimming pool now.
I would say the way he did it must be the best way to do it b/c look at his achievements; for sure the his dish is very accurate.

?????????? TO GERMAN SPEAKERS; have you read Tele-Satellite or forums' reports about Klaus Schumacher. -was his mould made of something CERAMIC ???

 

[freddy]

Concrete seems the best roue for a mould. Fix vertical pole in ground and shape concrete with cut out board swinging around pole. then seal & paint, then release compound ect. (perhaps woven rather than random fibre ?)

I seem to remember some years back on Tomorrows World an antennae based on diffraction rather than reflection? In the demo refraction was by a sries of concentric circles printed on adhesive plastic and stuck on a window, spacing of the rings and focus being the result of relatively simple math.
This always seemed to me to offer a simple way to build a LARGE antennae (and its on my list of things to do)

 

[divibi]

I seem to remember some years back on Tomorrows World an antennae based on diffraction rather than reflection? In the demo refraction was by a sries of concentric circles printed on adhesive plastic and stuck on a window, spacing of the rings and focus being the result of relatively simple math.
This always seemed to me to offer a simple way to build a LARGE antennae (and its on my list of things to do)

Thanks Freddy, I didn't know such a thing existed at all. Was it for terrestrial tv or satellite reception as well? How can we find out more?

Back to the parabolic dish. Freddie, what would you use as a reflective surface and how thick it needs to be to be on the safe side?

 

[BombedOne]

Yes, that book also lists such antennas that can be used in Ku band (made of rings) and has formulas for it's calculations. But making such rings really large and maintaining their coaxiality, while preserving open space between them would be much more harder.

Also, there are PA (Phased Array) antennas. You may have seen them around, they are so called flat satellite antennas. They also can be made @ home, but they have worst efficiency from available designs. They are just ok for areas with perfect coverage.

 

[Robbo]

For example, I can't see my post for couple of hours, nor I can find "attach the file" link.

You keep putting things in your posts that trigger the forum spam filter, putting your posts into a holding queue, until approved by a moderator or admin.

The $ symbol which catch you for example.


The reflective element of these fibreglass dishes is normally some sort of mesh or perforation I believe. I don't think the thickness is important, but the holes must be small enough not to let the microwaves through, if I remember correctly, less than 1/10 of the wavelength.

 

[divibi]

The reflective element of these fibreglass dishes is normally some sort of mesh or perforation I believe. I don't think the thickness is important, but the holes must be small enough not to let the microwaves through, if I remember correctly, less than 1/10 of the wavelength.

We really have to find out how Klaus Schumacher made his 8 metre dish. There is no better way than what he did.

 

[BombedOne]

I have been at satellite dish manufacturing plant, in early 90s. They were doing composite dishes. For reflective layer, they glued fine aluminum powder to dish surface, then polish it, and cover with paint. Unfortunately, I was only able to see that stage. I have no idea how dish themselves were made (they were huge prime focus ones, 3 and 5 meter).

 

[chucklebezza]

Theres quite alot about Klaus Schumacher on youtube. just put his name in and they will come up. very impressive

 

[BombedOne]

Well, regardless of way he did it - I'm not going to make 8m one anyways I just want to estimate, what will be cheaper - buy 2.4m one or make own 3m one.

Btw, I found very good mold for my small scale test. I have parabolic glass reflector of stadium projector. It's never used, and about 60cm in diameter. I guess, it solely can act as satellite antenna, but I'll use it as mold for my fiberglass dish.